Rotary lead-throughs of this type are well known. In these rotary lead-throughs, the seal between the covering plate and the bearing journal makes it possible for the conveyor roller to make-both axial movements and oscillating movements relative to the bearing blocks and the covering plate. In the first known rotary lead-through (EP 0 859 676 B1), the seal is a ring-shaped flange-like diaphragm made of a flexible material, connected on the one hand to the face of the bearing journal, and on the other hand to the bushing which is seated in the covering plate so as to provide a seal, and which delimits the ring channel. In the second known rotary lead-through (DE 197 52 336C1, DE 42 07 042 C1) the flexible seal comprises a flexible hose which on the one hand is connected to the bearing journal, and on the other hand to the sleeve which is seated in the covering plate. Both designs are associated with a disadvantage in that, due to the required ability to allow both axial movements and oscillating movements, they are complex in their design and installation, and due to their flexible components only have a limited service life.